Merge pull request #572 from juanriaza/master

Unused imports
Imply an additional element in infinite lists

This is to allow the addition of elements without
having to change existing lines of code
Some comment on the tutorial repository
Bringing up the Web API
Merge pull request #550 from Wackerbarth/tutorial

Revised Tutorial
Make the whitespace uniform
Merge pull request #573 from Wackerbarth/tutorial

Make the whitespace uniform
Added @wackerbarth.  Thanks!
Fix typo in permission_classes
auto_now and auto_now_add fields should be read only by default
PK fields should only be read-only if they are an AutoField.  Fixes #563
Update release notes.
Update django-filter link to pypi
Update django-filter link to pypi
Minor gramatical correction
Merge pull request #577 from Wackerbarth/tutorial

A minor gramatical correction
Format extensions have already been introduced.

If format extensions are used,
they must be used in the creation of the
reverse URLs.
Merge pull request #578 from Wackerbarth/tutorial

Format extensions have already been introduced.
Version 2.1.16
Add link to @mjumbewu's CSV package